Will Eliminating the Cats Cause the Check Engine Light to Come On?


ViperJoe

ViperJoe

GT Owner
Mark II Lifetime
Aug 17, 2006
1,305
Washington Crossing, PA
I understand that the Ford Racing header system eliminates the cats, but wouldn't that precipitate a check engine light? If so, is an electronic defeat device available? I had a dickens of a time eliminating the CE light when I removed the cats from my Viper (for racing purposes only I might add).

Aside from that, do the headers really free up that much more power on a stock engine? How about a lightly modified engine?
 
I can't speak for the GT, but the SuperSprint headers and metallic racing cats on my 2001 M5 (used for off road only) really freed up a lot of power. It was night and day. Dyno of 395.5 rwhp, compared to 325-330 rwhp stock. There were some other minor performance mods, but no engine work. The headers probably added 30+ hp alone.

Oh, and the sound with a Tubi Style exhaust, was very very sweet.

M5 was tuned at PowerChip directly in Santa Monica, and no SES problems.

However, the M5 race cats would simply not pass Smog sniff test. The HC levels were just too high, although all other indicators were fine. So, the cats were converted to be easily swappable with the factory cats.

(Not that Smog tests would be needed for an off road vehicle...)

And the bone stock GT did a great job on all aspects of Smog. Runs very clean.
 
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ACRJoe said:
Aside from that, do the headers really free up that much more power on a stock engine? How about a lightly modified engine?
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Most folks say 10-15 horsepower. I'm not aware of anyone doing a before and after dyno session on it.

It's more than worth it in weight and heat savings though, nevermind the "big balls" exhaust note.
 
Freeing up the breathing is what making horsepower is all about of course, because engines are just big air pumps. Doubly important on forced air induction motors. A regular normally aspirated engine can be expected to gain 30 -35 HP by bolting on headers (over stock cast manifolds); a 'blown' induction motor can expect double that.

Gotta check out - off for our monthly club morning blast through the mountain passes, before the radar cops wake up! Got my Valentine 1 just in case. See ya!
 
50 BMG said:
Most folks say 10-15 horsepower. I'm not aware of anyone doing a before and after dyno session on it.

It's more than worth it in weight and heat savings though, nevermind the "big balls" exhaust note.
Click to expand...

That seems lower than I would expect. The only way to know is with a baseline dyno and a dyno after, on the same or similar dyno equipment, and similar conditions (temp).
 
Yes it will go on . I gained 61 hp form my base run.
 
I understand that the Ford Racing header system eliminates the cats, but wouldn't that precipitate a check engine light? If so, is an electronic defeat device available? I had a dickens of a time eliminating the CE light when I removed the cats from my Viper (for racing purposes only I might add).
Click to expand...

ACRJoe,

Removing the cats will definitely trigger the CEL. The good news is that re-programming the ECU is VERY easy with the SCTII programmer. I installed the cat-less Ford Racing Rear Exit Headers AND the SCT engine program at the same time. The SCT program lets the ECU operate normally but eliminates the O2 check test. If you purchase your Rear Exit Headers from a competent source (I highly recommend Muscle Motors - a sponsor on this forum) they can provide you the SCT programmer along with the headers and you'll be all set.

I think 711's experience should be repeatable. In approximate terms, the headers combined with no cats should be good for ~25HP. Then you can have the benefit of a tune - which tweaks the car a little for the headers and removes a tad of the conservatism of the stock tune.

I'm going to dyno mine next week at Muscle. It would be great if we had a stock-exhaust vehicle so we could do a comparison. (I don't have a baseline as Muscle's dynois newly installed.)
 
If you did a search and read the old posts you would learn about a resistor that all speed shops use to fool the computer and the check engine light does not come on. Any decent speed shop will know about it, if they don't you are using the wrong speed shop.

Dave
 
barondw said:
If you did a search and read the old posts you would learn about a resistor that all speed shops use to fool the computer and the check engine light does not come on. Any decent speed shop will know about it, if they don't you are using the wrong speed shop.

Dave
Click to expand...

A point well made; then add to this that with all the code cracking that has been done with Ford’s PCM the idea of simply have the rear 02 sensor disabled (for off road use only) is a viable option as well.

The problem with leaving it on it one has no way of knowing what other issue may come up. This could lead to other issues.

With the cats gone the code is “Cat Inefficiently” which is a 0BDII issue and has no affect on the operation of the gals.

All the best

Shadowman
 
If anyone is interested, I purchased 3 of those resistors for my other car... but only used two of 'em.

That means I've got one extra as a sample that one of our electrical gurus could identify specs for us based on the color coding bands. If somebody wants to give it a try, I'll post up a pic.

mardyn
 
Post a picture and I will decode the resistor for all of us.

BlackICE
 
No worries, Gents,

however, get a proper tune (needed anyhow), and therein eliminate the check cat signal (simple) but don't forget to readjust the A/F settings...

Getting rid of the cat is generally a good thing (thermodynamically), as we have a forced induction block even more efficient to eliminate exhaust resistance. But you need to properly readjust settings, or you will most likely have even less power than before (can't believe I write 'even less', but so is it...) !

Enjoy,

Stefan

PS: once properly tuned, you will consume less fuel, btw..
 
How about some printouts from the dyno run's stock the after just the long tube install no tuning. The car is smarter than you think.
 
Ok my attachments are to large
 
Here ya' go on the resistor pic.
 
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That is a 75 ohm 5% tolerance resistor. Any size would work 1/4 watt is the smallest.

Here is a color chart.

http://engr.astate.edu/circuits/resistor-code1.jpg

BlackICE
 
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